The long term objectives of the study are to elucidate the origin and evolution of human immunodeficiency viruses (HIV). The current hypothesis that HIV originated from nonhuman primates in Africa may be flawed since the studies were not done in animals in their country of origin. The specific aims are: (1) to determine the prevalence of simian immunodeficiency virus (SIV) infection in free-living nonhuman primates in Liberia, West Africa, (2) to look for evidence of monkey to human transmission of SIV in West Africa, (3) to establish the antigenic interrelationships of SIV from primates in West Africa, (4) to determine the genetic diversity among SIV isolates from West African nonhuman primates, and (5) to compare the incidence of disease in SIV-free and SIV-infected sooty mangabey (SMs) colonies in Liberia and to determine the likely modes of natural transmission (mother to offspring, mating or other contact such as grooming or biting). In preliminary studies performed in Liberia, SIVsm was isolated from a sooty mangabey that was a household pet. In other preliminary studies, cloning of SIVsm from a captive-bred mangabey in the USA established that SIVsm, SIVmac and HIV-2 are a closely related sub-family of lentiviruses and that SIVsm is a probable source of the cross-species infection in humans that led to the emergence of HIV-2 in West Africa. In the proposed studies, cryopreserved blood cells and serum will be collected from free living monkeys and from pet monkeys to assess the prevalence of SIV in wild monkey troops and in household pet monkeys in all regions of Liberia. All wild monkeys will be released after tattooing and blood sampling. Identical studies are also proposed for African green monkeys and other species in Liberia. Thirty unwanted pet mangabeys will be used to establish breeding colonies of SIV-free and SIV-infected mangabeys to study pathogenesis, vertical and sexual transmission of SIVsm. Hunters and pet owners that have frequent physical contact with positive animals and with blood and tissues of freshly killed animals will be tested for SIV and HIV by immunoblot and virus isolation. Using 5-10 different isolates from each species, monoclonal antibodies will be prepared and molecular cloning done to establish antigenic and molecular interrelationships between monkey and human viruses obtained in West Africa; a family tree of these interrelationships will be constructed. An understanding of the origin and transmission of HIV is essential in prevention and the design of control measures for this complex disease.